The development of neuroprotective and neuroregenerative agents for dopamine neurons is viewed as a plausible objective for treating Parkinson's disease. Brain imaging of the dopamine transporter, localized almost exclusively on dopamine neurons, offers a potential window on the effectiveness of these agents. In 5 adult cynomolgus monkeys, PET imaging with the dopamine transporter probe [11C]WIN 35,428 (CFT) yielded a binding potential of approximately 2. After MPTP (3 x 0.6 mg/kg), all animals showed profound signs of Parkinsonism and a reduction of the binding potential to 0.1. Within 3 months, two monkeys exhibited signs of recovery, including weight gain and improvement in motor function. Most significantly, PET imaging of the dopamine transporter reflected these changes, as the binding potential of [11C]WIN 35,428 increased. These results may indicate that synaptic or axonal sprouting occurred during the recovery phase, although the latter is more likely in view of the time course of recovery. This novel finding suggests that PET imaging of the transporter may be an effective noninvasive method for assessing the therapeutic efficacy of therapies designed to prevent further degeneration of, or to promote regeneration of dopamine neurons. Madras BK T. Brackett, N. Alpert, A. Bonab, AJ Fischman. PET imaging of the dopamine transporter in Parkinsonian monkeys a